(a) Field of the Invention
This invention relates to a genuine black-color forming two-component type (or binary) diazo copying material suitable especially for preparing a secondary original used in electrophotographic copying machines.
(b) Description of the Prior Art
As conventional binary diazo copying materials capable of black-color forming, there are known those employing a blue-color forming coupler, such as .beta.-naphthol derivative, in combination with a yellow-color forming coupler, such as acetoamide derivative and phenol derivative. However, said acetoamide derivative useful as the yellow-color forming coupler is defective because it is higher in coupling speed than general couplers so that a copying material comprising these compounds is apt to cause precoupling with the diazo compound during prolonged storage, and when it is employed jointly with a .beta.-naphthol derivative, due to the difference of coupling speed between these two compounds, just a slight change of the developing conditions, that is, the developing temperature, the pH value of the developer solution, the amount of the developer solution attached, etc. would cause a change of the color tone of dye image, resulting in a failure to form a genuine black-color image. As to said phenol derivative for use as a yellow-color forming coupler, although it does not cause precoupling because it is lower in coupling speed than general couplers, when it is employed jointly with a .beta.-naphthol derivative, due to difference of the coupling speeds of the two compounds, the foregoing phenomenon would occur.
With a view to eliminating these defects, the present inventors have previously proposed the use of cyanoacetoamide derivatives as yellow-color forming couplers in Japanese Laid-open Application No. 126128/1976. However, a copying material comprising these compounds cannot produce a genuine black-color image, and the color tone of the resulting image is close to a green color. Therefore, especially the visual density of the half-tone area of the image is low, thereby making the copy indistinct. Further, in the case of preparing recopies from this copy by means of a commercial reflex-printing copying machine, such as an electrophotographic copying machine, there would occur the trouble that clear-cut recopies cannot be obtained.